Fuse and resistor device

ABSTRACT

A fuse and resistor device is disclosed comprising a substrate of insulating material, a resistance film of tin oxide deposited on said substrate, a layer of glass material having a relatively lower melting point and deposited on said resistance film and an insulation layer surrounding both said resistance layer and said glass layer. When overcurrent passes through the device it acts as a fuse resulting from the resistance film partially or wholly migrating into the glass layer now melted on the resistance film thus preventing the current from flowing through the device.

United States Patent [191 Takayasu et al.

[111 3,836,883 Sept. 17, 1974 FUSE AND RESISTOR DEVICE Inventors:Tatsunori Takayasu, Irima; Kouzi Higashi, Kaminiikawa, both of JapanHokuriku Electric Industry Co., Ltd., Toyama-Prefecture, Japan Filed:Dec. 6, 1972 Appl. No.: 312,500

7 Foreign Application Priority Data Dec. 8, 1971 Japan... 46-98713 June5,1972 Japan 47-55135 UIs'. 337/163, 337/159, 337/296 Int. Cl. H01h85/04 Field of Search 337/159, 160, 163, 296

Assignee:

References Cited UNITED STATES PATENTS 5/1973 Bucklin et a1 337/160Primary Examiner-J. D. Miller Assistant ExaminerFred E. Bell Attorney,Agent, or Firm-Watson, Leavenworth, Kelton & Taggart ABSTRACT 17 Claims,11 Drawing Figures BACKGROUND OF THE INVENTION This invention relates toa fuse and resistor device for an electrical apparatus and moreparticularly to a fuse and resistor device employed for incorporationinto an electrical circuit in an electronic communication apparatus,such as a television set or the like, and which acts as a normalelectrical resistor device during the passage of any rated currentthrough the device while the device acts as a fuse to abruptly interruptany overcurrent through the device when it passes through the circuit,whereby such overcurrent can be prevented from flowing through thecircuit. I

DESCRIPTION OF THE PRIOR ART Hitherto, any fuse and resistor device isimpractical because of its delayed development. In the prior art therehas been proposed a fuse and resistor device comprising a resistance orimpedance film in the spiral form on a substrate, said resistance filmincluding a portion of higher current density than that of the remainingportions thereof, which portion is adapted to be burnt off upon the flowof any overcurrent through the resistance film.

However due to the possible lack of uniformity in the width of thespiral resistance film along the spiral direction thereof, the fuse andresistor device will be partially overheated even during the passage ofthe rated current through the device, which causes it to have a worseload-life characteristic than that of a conventional film resistordevice and to have a gradually increased resistance value. Thus, suchfuse and resistor devices are practically speaking, unutilizable.

SUMMARY OF THE INVENTION Therefore, it is a principal object of thepresent invention to provide a fuse and resistor device which is adaptedto have a predetermined resistance value maintained during the flow ofthe rated current through the device and to assure the interruptionofovercurrent through the device.

Resistance film or layer oftin oxide, such as SnO has been usually usedfor a resistor device. The inventor has discovered that the tin oxideresistance film, when heated to high temperature, tends to be compatiblewith glass material, resulting from the same property of tin oxide tothat of glass material, which has been assured by many tests. It shouldbe understood that engagement of the tin oxide resistance film withglass material causes the resistance film to migrate into glass materialthere adjacent when subject to the high temperature to maximize theresistance value of the film.

In accordance with the present invention, there is provided a fuse andresistor device comprising a substrate of insulating material such asceramics, a resistance film of tin oxide deposited on said substrate, alayer of glass material having a relatively lower melting point anddeposited on said resistance film and an insulation layer surroundingboth said resistance layer and said glass layer. During the passage ofthe rated current through the device, it acts as a normal resistordevice and when overcurrent passes through the device, it acts as a fuseresulting from the resistance film partially or 2 wholly penetratinginto the glass layer to interrupt the current from flowing through thedevice.

BRIEF DESCRIPTION OF THE DRAWINGS The other objects and features of thepresent invention will be apparent to those skilled in the art from thereading of the following description of the preferred embodiments takenin connection with the accompanying drawings:

FIG, 1 is a side elevational view of a fuse and resistor device inaccordance with the present invention with an insulating layer brokenaway;

FIG. 2 is an enlarged and vertically sectional view of a portion of thedevice as shown in FIG. 1 with the arrangement of a glass layer shownrelative to a substrate and a resistance film;

FIGS. 3A through 3C are enlarged and fragmentary views in sectionshowing islet particles of resistance material gradually migrating intothe molten glass layer when overcurrent flows through the device asshown in FIG. 1, with FIG. 3C illustrating the resistance filminterrupted at a point of the resistance film where the islet particlesof resistance material migrate into the glass layer;

FIG. 4 is an elevational view of a modified fuse and resistor device inaccordance with the present invention with an insulation layer and aglass layer partially broken away;

FIG. 5 is an enlarged and fragmentary sectional view of anotherembodiment in accordance with the present invention;

FIGS. 6A and 6B are similar to FIG. 5, but showing islet particles ofresistance material gradually migrating into a molten glass layer whenovercurrent flows through the device as shown in FIG. 5, with FIG. 6Billustrating the device interrupted at a point of a resistance filmwhere the resistance film partially migrate into the glass layer;

FIG. 7 is a graph showing time required to interrupt various fuse andresistor devices in accordance with the present invention, relative toelectric power applied across the terminals of the devices; and

FIG. 8 is a graph showing the relationship of concentric current throughthe device as shown in FIG. 5 with time from the begining of theovercurrent to flow through the device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1, afuse and resistor device in accordance with the present invention isgenerally illustrated at reference numeral 1. This fuse and resistordevice is of a type referred to as a film resistor and comprises asubstrate 2 of insulating material such as ceramics, glass or the likeand resistance film or layer 3 of tin oxide deposited on the substrate 1by any conventional and suitable process. The processes for depositingthe resistance film include immersing, spraying, vacuum-depositing,sputtering, coating and the like. The'resistance film 3 may bepreferably formed of tin oxide including Sb O in addition to SnO The tinoxide resistance material may preferably include to 99.5 percent byweight of SnO and 0.5 to 10 percent by weight of Sb O The resistancematerial may further include tin polyoxide such as Sn O added thereto.

The resistance film 3 is shown to be conventionally cut into the spiralform to adjust the resistance value thereof to provide a predeterminedone. The device also comprises a pair of cap type terminals 4 and 4surrounding and securely mounted on both ends of the resistance film 3on the substrate 1 by conventional means, said terminals each having alead secured thereto at their centers by soldering or any other means.

The device comprises a layer 6 of glass material in the particle formhaving a relatively lower melting point and deposited on the resistancefilm 3, which should be understood to be the most important feature ofthe present invention. Commercial glass material may be used whichconsists of the following components, for example:

(Figures in this table indicate the extents of the components at percentby weight.)

The glass layer 6 may be partially applied on the spiral resistance film3 across one or two turns thereof as shown in FIGS. 1 and 2 because thedevice is sufficiently interrupted only at a portion of the resistancefilm 3. However, in view of the ease of its manufacture, it may bepreferably provided on the resistance film 3 over all the areas thereof.It should be noted that the time required to interrupt the device fromthe begining of the overcurrent flow through the device depends upon thearea of the glass layer 6 in contact with the resistance film 3 whichwill be described in detail hereinafter. The glass layer 6 may be bondedonto the resistance film 3 by any suitable adhesive added to glassmaterial of the layer 6.

An insulation layer 7 formed of material such as silicone is provided tocover the resistance film 3 and the glass layer 6 for retention of thelatter. The insulation layer may be preferably formed of non-combustiblematerial such as inorganic material and silicone resin when it issubject to high temperature, 300 to 800C, for example to which thedevice will reach as overcurrent passes therethrough.

The resistance film 3 of the present device, as shown in FIG. 3A,comprises a plurality of islet particles 3a superimposed one on another,said islet particles formed of aggregate crystals with the crystalsbeing bonded to each other by Van der Waals force which they have. Whenovercurrent passes through the tin oxide resistance film to cause thesurface thereof to reach the temperature of 300 to 800C, the glass layer6 on the film melts into fluid so that the islet particles 3a of thefilm 3 are absorbed or scattered into the molten glass layer in a shorttime as shown in FIG. 38 until all the islet particles 3a in contactwith the glass layer 6 are transferred into the latter as shown in FIG.3C. Thus, the spiral resistance layer 3 discontinues at a portionthereof to interrupt the passage of the overcurrent.

As previously mentioned, the time required to interrupt the passage ofthe overcurrent depends on the contact area of the tin oxide resistancefilm 3 with the glass layer 6. In case ofthe deposition of the glasslayer 6 on the resistance film 3 at a smaller area as shown in FIGS. 1and 2, upon flow of the overcurrent through the film 3, the isletparticles 3a of the layer 3 in contact with the glass layer 6 areshortly transferred into the latter to abruptly increase the resistancevalue of the device so that the film 3 provides an acceleratedlyincreased resistance value to enhance the interruption of theovercurrent through the device. On the other hand, in case of thedeposition of the glass layer 6 on the resistance film 3 at a largerarea as shown in FIG. 4 the islet particles 3a over the larger areamigrate into the glass layer 6 so that the film never provides a locallyincreased resistance value along the length thereof to tend to retardthe interruption of the overcurrent through the device. The interruptiontime depends also upon the thickness of the insulation layer 7 becausethe thickened layer prevents the heat from the resistance film 6 fromreadily dissipating thus increasing the temperature within the device.Thus, it will be found that a shorter interruption time can be providedby depositingthe glass layer 6 on the tin oxide resistance film 3substantially at its middle portion and thickening the insulation layer7.

Referring now to FIG. 5 there is illustrated in enlarged section aportion of a more preferable fuse and resistor device 11 wherein a blendlayer 16 is deposited either partially or wholly on a tin oxideresistance film or layer 13 in the spiral form on an insulatingsubstrate 12, said blend layer being formed of a blend consisting ofglass frits 16a and metal powder 16b, both of which are required to havelower melting points. The glass frits 16a may be of that compositiondescribed in connection with the previous embodiments as shown in FIGS.1, 2 and 4. Metal material in the form of powder 1612 includes indium,tin, cadmium, bismuth, lead, zinc and eutectic alloy thereof. The metalpowder may be preferably of the grain size in diameter less than 500microne. The metal powder may be preferably blended within a rangebetween 5 and 200 parts relative to parts of glass frits. Glass frit 16aand metal powder 16b may be bonded to one another by a binder, anorganic resin such as epoxy resin, melamine resin, phenol resin or aninorganic resin such as silicone, for example.

Such metal powder 16b serves to enhance the interruption time of thefuse and resistor device for the reason as described hereinafter. Whenovercurrent passes through the device as shown in FIG. 5 to reach highertemperature within the device, metal powder 16b in the blend layer 16are initially melted to be absorbed into the resistance film 13, asshown in FIG. 6A, so that a spark is established across the groovedefined by the spiral resistance film 13 to cause the concentric currentto flow thereacross. Thus, the concentric current flows through theresistance film 13 already heated by the overcurrent therethrough toraise the film to higher temperature than that it reaches when onlyovercurrent flows through the film as done in the previous embodimentsas shown in FIGS. 1, 2 and 4. Metal powder 16 (b) may most preferablyconsist of eutectic alloy of 74 percent by weight of indium and 26percent by weight of cadmium or that of 67.75 percent by weight ofcadmium and 32.25 percent by weight of tin.

FIG. 7 shows the relationship of the interruption time (the period fromthe begining of the passage of the overcurrent to the interruptionthereof) with the load power (rated power multiplied by the figuresindicated in this figure) in connection with specified examples inaccordance with the present invention, which were tested by theinventors. In this test there were used the devices in each of which theglass layer was of that listed in the first column (I) of theabove-indicated table and the insulation layer of silicone had thethickness of 1 mm. The devices used each had the resistance value of 50ohm per square, but it was found that other fuse and resistor devices ofdifferent resistance value had the same tendency to those of theexamples in this test. The characteristics indicated at the curves a1,a2 and 03 in FIG. 7 were those of the devices in each of which the layerof only glass material was provided on the spiral resistance film of tinoxide as shown in FIGS. 1, 2 and 4, while the characteristic indicatedat the curve b in FIG. 7 was that of the device in which the blend layerof glass material and metal powder was provided on the spiral resistancefilm identical to those of the devices having the characteristics a1, a2and a3. The resistance films used were each formed of material including95 percent by weight of SnO and 5 percent by weight of Pb O In thisfigure, the curve a 1 shows the characteristic of the device in whichthe glass layer was deposited on the spiral resistance layer across oneturn thereof as shown in FIG. 1, the curve a2 the characteristic of thedevice in which the glass layer was provided in the straight line on theresistance film along the longitudinal axis of the device, and the curvea3 the characteristic of the device in which the glass layer wasprovided on the resistance film over all the area thereof as shown inFIG. 4. As apparent from these curves, the smaller contact area theglass layer has with the resistance layer, the shorter the interruptiontime is. The curve shows the characteristic of the device in which theblend layer of 100 parts of glass frits and 100 parts of commerciallyavailable lead-zinc alloy powder bonded by 10 parts of epoxy binder wasprovided on the spiral resistance film across one turn thereof asarranged similarly to the glass layer as shown in FIG. 1. Ascomparedwith the characteristic indicated at the curve 02 which corresponds tothe curve b in the arrangement, the interruption time according to thecharacteristic indicated at the curve b will be found to besubstantially half of that of the former. It will be understood fromFIG. 8 that the current flows through the resistance film as shown inFIG. 5 within the range of to 40 seconds from the begining of thepassage of the overcurrent, about twice of that through the resistancefilm of the device as shown in FIG. 1 because of the concentric currentflowing through the former film.

It should be noted that the insulation layer not shown on the blendlayer and on the resistance film of the device as shown in FIG. 5 servesto prevent the explosion upon the establishment of the spark across thegroove defined by the adjacent turns of the spiral resistance film inaddition to protect the device from the circumferences thereof.

Some preferred embodiments of the present invention having beendescribed by way of example, it is anticipated that certainmodifications or changes in arrangement and construction mayoccur tothose skilled in the art, and it is anticipated that such alterationsand modifications may be made without departing from the spirit of theinvention or the scope of the appended claims.

What is claimed:

1. A fuse and resistor device comprising a substrate of insulatingmaterial, a resistance film of tin oxide deposited on the substrate, aglass layer having a relatively lower melting point deposited on theresistance film and an insulation layer surrounding both the resistancefilm and the glass layer, said resistance film being composed of tinoxide comprising a small amount of Sb O; in addition to SnO 2. A fuseand resistor device as set forth in claim 1, wherein said glass layer isin contact with said resistance film at a portion thereof.

3. A fuse and resistor device as set forth in claim 1, wherein saidglass layer is in contact with said resistance film over all the areasthereof.

4. A fuse and resistor device as set forth in claim I, wherein SnO isranged from to 99.5 percent by weight and Sb O is ranged from 0.5 to 10percent by weight.

5. A fuse and resistor device as set forth in claim 1, wherein saidresistance film is composed substantially of Sn O 6. A fuse and resistordevice as set forth in claim 4, wherein the thickness of said insulationlayer is predetermined to provide a reduced rate of dissipation of theinternal heat of the device and an increase in the internal temperatureof the device.

7. A fuse and resistor device comprising a substrate of insulatingmaterial, a resistance film of tin oxide deposited on said substrate, alayer of blend comprising glass material and metal material in the formof powder, both having a relatively lower melting point, said blendlayer deposited on said resistance film, and an insulation layersurrounding both of said resistance film and said blend layer.

8. A fuse and resistor device as set forth in claim 7, wherein saidmetal material is selected from the group consisting of indium, tin,cadmium, bismuth, lead, zinc and eutectic alloy thereof.

9. A fuse and resistor device as set forth in-claim 8, wherein saidmetal material is eutectic alloy of 74 percent by weight of indium and26 percent by weight of cadmium.

10. A fuse and resistor device as set forth in claim 8, wherein saidmetal material is eutectic alloy of 67.75 percent by weight of cadmiumand 32.25 percent by weight of tin.

11. A fuse and resistor device as set forth in claim 7, wherein saidblend layer is in contact with said resistance film at a portionthereof.

12. A fuse and resistor device as set forth in claim 7, wherein saidblend layer is in contact with said resistance film over all the areasthereof.

13. A fuse and resistor device as set forth in claim 7, wherein saidresistance film is composed of tin oxide comprising a small amount of SbO in addition to SnOg- 14. A fuse and resistor device as set forth inclaim 13, wherein SnO is ranged from 90 to 99.5 percent by weight and SbO is ranged from 0.5 to 10 percent by weight.

15. A fuse and resistor device as set forth in claim 7, wherein saidresistance film is comprised substantially of Sn O 16. A fuse andresistor device as set forth in claim 8, wherein the thickness of saidinsulation layer is predetermined to provide a reduced rate ofdissipation of the internal heat of the device and an increase in theinternal temperature of the device.

17. A fuse and resistor device as set forth in claim 7, wherein saidmetal material is blended within the range between 5 and 200 partsrelative to parts of glass material.

2. A fuse and resistor device as set forth in claim 1, wherein saidglass layer is in contact with said resistance film at a portionthereof.
 3. A fuse and resistor device as set forth in claim 1, whereinsaid glass layer is in contact with said resistance film over all theareas thereof.
 4. A fuse and resistor device as set forth in claim 1,wherein SnO2 is ranged from 90 to 99.5 percent by weight and Sb2O3 isranged from 0.5 to 10 percent by weight.
 5. A fuse and resistor deviceas set forth in claim 1, wherein said resistance film is composedsubstantially of Sn2O3.
 6. A fuse and resistor device as set forth inclaim 4, wherein the thickness of said insulation layer is predeterminedto provide a reduced rate of dissipation of the internal heat of thedevice and an increase in the internal temperature of the device.
 7. Afuse and resistor device comprising a substrate of insulating material,a resistance film of tin oxide deposited on said substrate, a layer ofblend comprising glass material and metal material in the form ofpowder, both having a relatively lower melting point, said blend layerdeposited on said resistance film, and an insulation layer surroundingboth of said resistance film and said blend layer.
 8. A fuse andresistor device as set forth in claim 7, whereIn said metal material isselected from the group consisting of indium, tin, cadmium, bismuth,lead, zinc and eutectic alloy thereof.
 9. A fuse and resistor device asset forth in claim 8, wherein said metal material is eutectic alloy of74 percent by weight of indium and 26 percent by weight of cadmium. 10.A fuse and resistor device as set forth in claim 8, wherein said metalmaterial is eutectic alloy of 67.75 percent by weight of cadmium and32.25 percent by weight of tin.
 11. A fuse and resistor device as setforth in claim 7, wherein said blend layer is in contact with saidresistance film at a portion thereof.
 12. A fuse and resistor device asset forth in claim 7, wherein said blend layer is in contact with saidresistance film over all the areas thereof.
 13. A fuse and resistordevice as set forth in claim 7, wherein said resistance film is composedof tin oxide comprising a small amount of Sb2O3 in addition to SnO2. 14.A fuse and resistor device as set forth in claim 13, wherein SnO2 isranged from 90 to 99.5 percent by weight and Sb2O3 is ranged from 0.5 to10 percent by weight.
 15. A fuse and resistor device as set forth inclaim 7, wherein said resistance film is comprised substantially ofSn2O3.
 16. A fuse and resistor device as set forth in claim 8, whereinthe thickness of said insulation layer is predetermined to provide areduced rate of dissipation of the internal heat of the device and anincrease in the internal temperature of the device.
 17. A fuse andresistor device as set forth in claim 7, wherein said metal material isblended within the range between 5 and 200 parts relative to 100 partsof glass material.